In the prior art, after a Mobility Management Entity (MME) is restarted, a User Equipment (UE) in an idle mode cannot detect the loss of established Packet Data Network (PDN) connection(s) until it initiates any TAU or Service Request procedure, by that TAU or Service Request procedure, the UE will be triggered to reattach onto the network. If the UE had any network service, e.g., an IP multimedia system voice call, before the UE reattaches to the network, then this downlink service would be rejected because there is no context of the UE on the MME.
In order to address the problem arising from the MME restart, two solutions have been proposed respectively as follows:
First Solution:
When the MME receives a TAU/Routing Area Update (RAU) request of the UE, the MME checks a Tracking Area (TA) List and determines whether it needs to be updated, and if the list needs to be updated and the UE has at least one Downlink Data Triggered Attach (DLDTA) bearer (as assumed in this method, based on the operator's configuration, for some bearers on S5/S8 interface of the UE, as long as they have downlink data, paging has to be triggered to recover the PDN connection(s) and guarantee user experience, even if the MME is restarted), then the MME has to notify the Serving Gateway (SGW) to update the stored TAI list by a Modify Bearer Request message (C4—101741: When MME receives the TA update request/RA update request message from UE, then MME checks if the TA-list information needs to be updated or not. If the TA-list needs to be updated and the UE has at least one DLDTA bearer, then MME sends the Modify bearer request message ( . . . , TA-list/RA)), so that the SGW maintains the updated TAI list. after the MME is restarted, the SGW knows that the MME is restarted according to echo mechanism or like that, and at this time, the SGW decides to reserve some of the hearers on an S5/S8 interface as configured by the operator, and when downlink data arrive over these hearers, the SGW triggers paging and also will carry the stored latest TAI list of the UE in the downlink data notification to the MME. The UE will reattach to the network upon reception of a paging message carrying an International Mobile Subscriber Identity (IMSI).
Second Solution:
In session establishment and modification procedures, the MME will notify the SGW of the latest updated TAI list (C4—101767: During the session establishment and modification procedures, the MME transfers the latest TAI list of the UE to the SGW), and after the MME is restarted, the SGW knows in an echo mechanism or like that the MME is restarted, and at this time, the SGW triggers paging and also carries all the TAI lists of UEs related to the MME in a downlink data notification to the MME, the MME pages all the UEs, and the UEs are reattached to the network and reestablish all the PDN connections upon reception of a paging message carrying an IMSI.
Drawbacks of the prior art at least lie in that:
The two solutions may not satisfy a demand for updating a TAI list; and
The two solutions may not necessarily enable a TAI list to be updated.